1. Field of the Invention
This invention relates to an image viewing station for picture archiving and communications systems (PACS), and more particularly to such a station for processing and displaying digital diagnostic images.
2. Discussion of the Background
In recent times, escalating health care costs have spurred efforts to make health care delivery systems less expensive and more efficient, particularly in hospitals. This has led to the introduction of computers in many areas of hospital management. Computers have been used for many years in areas such as patient registration and in clinical laboratories. A major new application area is within radiology departments.
Modern radiology systems will consist of two major components. The first component consists of a system to provide management tools such as scheduling and inventory control. The second component is a system to replace the film based imaging systems currently used in radiology departments with their photoelectronic equivalents. This application area is called PACS (Picture Archiving and Communication Systems).
A PACS system can be divided into several subsystems as shown in FIG. 1.0. They are photoelectronic image acquisition 2, image storing or archiving 4, electronic image transmission 6, image display 8, and external communication links 9. The specification of each of these components is a function of the number of images generated, the resolution of these image, and the number of times each image is viewed.
Chest radiographs comprise about 85% of the total case load in a radiology department. They are also the most difficult class of images to handle. These images are characterized by a spatial resolution of at least 2048.times.2048 pixels with a 60 db dynamic range. Thus, each chest radiograph requires about 40 megabits for representation. To transmit such an image from an archive to a display workstation in 0.5 seconds (time requirements to be discussed below) requires a transmission bandwidth of more than 80 megabits/sec. To display such an image on a video monitor (with a single gun CRT) requires that data be presented at an 2.8 megapixel rate. These requirements underscore the difficulty in processing a chest radiograph within a PACS environment. Since a large percentage of a radiology department's work load involves the generation and diagnostic evaluation of chest radiographs, a successful PACS system obviously must be able to accommodate the vast amounts of image data forthcoming from the chest radiographs.
The first of the PACS subsystems is the photoelectronic image acquisition system 2. Many medical imaging modalities already produce images in digital form. These include Computed Tomography (CT), Nuclear Medicine, Magnetic Resonance Imaging (MRI), Ultrasound and Digital Subtraction Angiography. These images are characterized by spatial resolution 512.times.512 or less, with 40 to 60 db dynamic range. Until recently there was no photoelectronic system capable of acquiring large format (14.times.17 inch) images such as those of the chest. Without this large format capability, a PACS system would be of little value since these images comprise such a large percentage of all those taken. The introduction of large format image acquisition systems eliminates the last major PACS specific data acquisition problem.
The second PACS subsystem is image archiving 4. There are many approaches to this problem. The current strategy is to divide the archive into two sections. The first, a short term archive, is designed to handle the active images for patients currently under treatment. It is characterized by rapid access time, read/write capability, and limited storage. The long term archive is non-erasable. Laser optical disks are being proposed for this application. The current technology will provide approximately three gigabytes of storage on a ten inch diameter disk. The combination of these two technologies will provide for both rapid access to active images and compact long term storage.
The third PACS subsystem is image transmission 6. The transmission system must provide bidirectional communication between acquisition systems, display workstations, and the image archive. It is envisioned that this system will eventually become a component of a national network 9 linking together hospitals all across the country. The primary design considerations for the image transmission system are speed and reliability. Speed is being achieved through the use of parallel fiber optic transmission links. Reliability is achieved through redundant data paths. The systems are designed such that a single cable failure will have only local effect.
The fourth PACS subsystem and the subject of this invention, is the digital image viewing workstation 8. This workstation will functionally replace the large panels of light boxes currently used with the film based imaging system.
Radiologists consume information at an incredibly large rate. In a typical situation, six to eight images will be examined and the report dictated in less than a minute. To meet the needs of the PACS system, and to be accepted by the medical community, the viewing workstation must provide image handling no slower than that of the film system it is designated to replace.